Based on the GSM module TC35 smart gated security system design (1)

Introduction

With the improvement of living standards and security conscious, people began to care about their own lives and the working environment, not only the requirements surrounding environment a comfortable and user-friendly, on the working environment of security and intelligence also place high demands on the security system has become an indispensable part of life.

Traditional security systems rely primarily on the telephone network broadcast warning messages, but phone NetEase was damaged, and does not apply to remote areas, such as the erection of communication lines or not economic.

The GSM network is based on TDMA technology and frequency division multiple access technology communication network system, is China's most extensive coverage, the most powerful, most digital cellular mobile communication network.

By China Mobile company built a seamless nationwide GSM network, using GSM technology transfer police call information, have a safe, reliable, and easy installation.

1. system structure and principle

This security system structure as shown in Figure 1.

Various alarm sensors are installed in different locations, as an exception, the corresponding sensor wireless signal will be sent to the control module of the wireless receiver circuit, control module through the software determines that the exception type, through the serial port control sends the appropriate GSM module alarm SMS, after a few seconds, the user's mobile phone can receive a warning message to remind the user to take measures. When a user in the site, you can send SMS to remove alarm function (hereinafter referred to as a garrison), prevent the action of alarm on users to false alarms. You can use your computer for storage in the EEPROM of alarm records for reading, and set the alarm system.

2, hardware design

2.1 wireless alarm sensor

Wireless alarm sensor including Pyroelectric passive infrared detectors, smoke detectors, gas leak alarm, Windows (Mun) magnetic detectors, etc.

Each wireless alarm sensors are sensors, signal processing circuits, wireless transmitter, etc. The sensor detects an exception case, through the wireless transmitter for wireless alarm. In order to differentiate between the type of alarm (i.e. Aviso type), while enhancing system anti-interference ability, improve the accuracy of the alert, each alarm can have a different encoding. This code consists of the "access code" + "ID code", "access code" is used to indicate different security system, the same security system, all wireless alarm code and wireless receiver circuit code is the same; " Status codes "used to indicate different wireless alarm sensor. You can access code and status codes, such as a hardware implementation using SC2262 coding chip and SC2272 decoding chip implementation; or is realized through software, in programming is written directly to the address mask and identity code.

2.2 control module

Control module is the core PIC16F74 microcontroller.

PIC16F74 is a low-power, high speed flash microcontroller, internal USART major integration module, I2C bus, SPI interface, input capture/output compare/PWM CCP module, A/D converters, watch dog timer WDT features. PIC16F74 has 35 simple instruction set, which in addition to the programs branch instruction is a single-byte and two-cycle instructions, are single-byte and single-cycle instructions. Single-byte wide directive improves software coding efficiency, reduces the need for the program memory modules, the system has very high efficiency and excellent performance. PIC16F74 SCM exceptional performance combined with good electromagnetic compatibility characteristics, making it ideal for the development of this system. Control module is used primarily to handle the alarm information, and communication with the PC. SCM and real-time clock chip (SD2001) communicate via I2C interface. SCM through common IO and EEPROM (AT24C16) communication, AT24C16 to I2C interface, read and write to it, having microprocessor programs produce I2C timing. EEPROM in addition to storing the alarm message, also stores the user's mobile phone number and a garrison of the password.

2.3 MCU and GSM module, PC hardware interface circuit

Figure 2 shows the MCU and TC35, PC connection diagram.

GSM module adopts Siemens TC35 introduced. TC35 is a high-performance GSM module, in application of the system is very easy to integrate, can work in GSM900kHz and 1800kHz two band, RS-232 data interface, in compliance with ETSI standard GSM07.07 and GSM07.05, and easy to upgrade to GPRS (General packet radio services) module. TC35 set RF Circuit and baseband, provide the user with the standard AT command interface for data, voice, SMS, fax, provides fast, secure, reliable transmission, user-friendly applications development and design.

　　

As a result of the work in TC35 data interface CMOS level, and work in TTL level PIC16F74, operating voltage range is generally lower than TC35 width should be between the microcontroller and TC35 with level conversion circuit.

SCM through asynchronous serial interface RC6 to RC7 and TC35, data communication, communication speed, use s 9600kbit/8 bit asynchronous communication means, 1 start bit, 8 data bits, 1 stop bit.

Microcontroller using common IO and PC serial port communications.

SCM needs in communication program generation serial sequence. [1] [2] [3]